When one of two cross-wound packages of a single feed yarn is unwound on a two-for-one twisting spindle, the following situation will primarily arise with respect to the yarn ends.
Only in relatively rare cases will it be possible to adapt the yarn lengths of the two cross-wound packages inserted into a two-for-one twisting spindle one to the other in such an accurate manner that they also unwind simultaneously, and that thus only the unwound tubes remain in the twisting spindle. Predominantly, one has to assume that while one package is fully unwound, some yarn is still left on the second package.
During the two-for-one twisting process, the twisted yarn is subjected in the yarn balloon to a constantly high tension corresponding to the yarn count and the spindle speed. When, after the complete unwinding of one feed yarn package, only one yarn component continues to pass through the yarn balloon, same will normally not withstand the yarn tension, and will tear. Should this not occur, monitoring devices are arranged in the further yarn path, which detect the single yarn, trigger a corresponding signal and either stop the spindle or, however, retain the yarn by clamping as it enters into the spindle, or inside the spindle.
This remaining and broken single yarn, which advances from the upper or the lower feed yarn package, continues to proceed to the apex of the hollow spindle shaft, advances through the hollow spindle shaft, and terminates mostly on the external rim of the spindle rotor on the storage disk.
When now an empty or almost empty unwinding unit is removed from the two-for-one twisting spindle (no matter whether by hand or a handling device), the yarn end, which is pulled out of the hollow spindle shaft, will fly freely and vagabond from the center of the creeling device (adapter).
In the further handling of the unwinding unit, the freely flying yarn will not only be a hazard, for example, to the two-for-one twisting spindles operating in the direct vicinity, but also for the handling and motional operations within a maintenance and handling device.
Likewise unsecured is the yarn end, which is located between the wind on the package and the apex of the adapter, and same may loosen as a result of external circumstances such that it will cause impediments.
However, yarns twisted by the two-for-one twisting process are also made from an assembly wound feed yarn package. The two yarn strands which participate in the twisted yarn, are previously doubled (plied) on an assembly winder and wound onto a single package.
Normally, one can presume that the assembly-wound packages unwind completely and that therefore no yarn remnants are left on the assembly winding tube. However, practice shows, that shortly before the complete unwinding of an assembly wound package, yarn remnants are occasionally left on the tube. The reason therefor is to be found in the initial winding on the assembly winder, where the initial yarn layers often engage with one another. The consequence is a yarn break on the two-for-one twisting spindle and thus a yarn remnant on the assembly winding tube.